1. Field of the Invention
The present invention relates to a single-lens reflex digital camera capable of displaying live view.
2. Description of the Background Art
There is a type of single-lens reflex digital camera capable of displaying live view on a liquid crystal display monitor. A photographer looks for the right time to take an image while seeing a real-time image displayed on the liquid crystal display monitor. In recent years, the size of the liquid crystal display monitor is increased so that operability of the single-lens reflex digital camera having a live view display function is improved.
In the single-lens reflex digital camera, ingenious attempts have to be made to realize live view display. On the other hand, in a compact digital camera, a light from a subject is always incident on an imaging element for imaging an image for storage so that an output from the imaging element can be utilized for live view display.
In the single-lens reflex digital camera, however, the light from the subject is reflected by a movable mirror (reflex mirror) and guided to a finder before imaging operation. Therefore, the light from the subject is not incident on the imaging element for imaging the image for storage before imaging operation.
There is a single-lens reflex digital camera separately including the imaging element for imaging the image for storage and the imaging element for imaging the image for live view. FIG. 6 is a block diagram showing a conventional type of single-lens reflex digital camera 100 including two imaging elements.
The single-lens reflex digital camera 100 includes two CCDs 101 and 102. The CCD 101 is the imaging element for imaging the image for storage, and the CCD 102 is the imaging element for imaging the image for live view. The single-lens reflex digital camera 100 also includes a LSI 110, a memory card 117, a LCD 118, and a main memory 120.
The LSI 110 includes a selector 111, an image preprocessing unit 112, an image general processing unit 113, a display control unit 114, a JPEG processing unit 115, and a card controller 116.
The selector 111 inputs pixel signals output from the CCDs 101 and 102 and outputs the input pixel signals from either the CCD 101 or the CCD 102 to the image preprocessing unit 112.
A process executed when the image preprocessing unit 112 inputs pixel signals output from the CCD 101 will be described. That is to say, a series of process steps for the image for storage will be described. The image preprocessing unit 112 executes processings of correction of defective pixel, black level difference operation, or the like, to generate RAW image data 131. The image preprocessing unit 112 stores the generated RAW image data 131 in the main memory 120.
The image general processing unit 113 reads the RAW image data 131 stored in the main memory 120 and executes image processings of pixel interpolation process, gamma conversion process, color space conversion process, or the like, to generate YUV data for storage 133. The image general processing unit 113 stores the generated YUV data for storage 133 in the main memory 120.
The JPEG processing unit 115 reads the YUV data for storage 133 stored in the main memory 120 and executes JPEG compression coding to generate JPEG data 134. The JPEG processing unit 115 stores the generated JPEG data 134 in the main memory 120.
The card controller 116 reads the JPEG data 134 stored in the main memory 120 and writes into the memory card 117. By executing such a series of process steps, the JPEG data 134 is written into the memory card 117 as the imaged image data for storage.
Next, a process executed when the image preprocessing unit 112 inputs pixel signals output from the CCD 102 will be described. That is to say, a series of process steps for the image for live view will be described.
The image preprocessing unit 112 executes processings of pixel interpolation process, gamma conversion process, color space conversion process, or the like as well as processings of correction of defective pixel, black level difference operation, or the like, to generate YUV data for display 132. The image preprocessing unit 112 stores the generated YUV data for display 132 in the main memory 120. Thus, the image preprocessing unit 112 includes process blocks for executing processings of pixel interpolation process, gamma conversion process, color space conversion process, or the like, in order to generate YUV data for display 132. Process blocks including relatively simple functions compared to those included in the image general processing unit 113 are provided as these process blocks.
The display control unit 114 reads the YUV data for display 132 stored in the main memory 120 and outputs the data to the LCD 118.
Inclusion of the two CCDs 101 and 102 as described makes recording of the imaged image data for storing in the memory card 117 and display of live view image on the LCD 118 possible. However, the pixel signal output from the CCD 102 cannot be read into the image preprocessing unit 112 while the image preprocessing unit 112 reads the pixel signal from the CCD 101 and the image preprocessing unit 112 executes image processings onto the pixel signal output from the CCD 101. Therefore, live view display is stopped until transfer and image processings of the pixel signal for storage are completed. The mechanism of this operation will be described with reference to FIG. 7.
FIG. 7 is a diagram showing a process sequence when the single-lens reflex digital camera 100 executes continuous imaging process (hereinafter, the continuous imaging process is appropriately referred to as continuous shooting). A signal B1 represents a signal controlling opening and closing operations of the movable mirror. “Open” in FIG. 7 indicates a state where the movable mirror is raised up, that is to say, a timing at which the light from the subject is incident on the CCD 101. “Close” in FIG. 7 indicates a state where the movable mirror is closed, that is to say, a period during which the light from the subject is incident on the CCD 102. A signal B2 represents a vertical synchronizing signal (VD) of the CCD 101.
A timing flow B3 represents a timing at which the CCD 101 exposes a still image (image for storage) to light. A timing flow B4 represents a timing at which the image preprocessing unit 112 reads the pixel signal from the CCD 101 and a timing at which image processings are executed in the image preprocessing unit 112. A timing flow B5 represents a timing at which the image general processing unit 113 executes image processings on the RAW image data 131 and a timing at which the JPEG processing unit 115 executes JPEG compression process on the YUV data for storage 133. A timing flow B6 represents a timing at which the card controller 116 stores the JPEG data 134 in the memory card 117. Then, a timing flow B7 represents a timing at which the image for live view output from the CCD 102 is displayed in the LCD 118. At the timing flow B7, “On” indicates a timing at which live view is displayed and “Stop” indicates a timing at which live view display is stopped.
It is to be noted that “1st”, “2nd”, and “3rd” in FIG. 7 indicate processes for first, second, and third still images, respectively, during continuous shooting.
Live view is displayed before first “Open” operation of the movable mirror as shown in FIG. 7. Along with the first “Open” operation of the movable mirror, the CCD 101 exposes a first still image to light. During this period, live view display is stopped because the light from the subject is not incident on the CCD 102.
Then, along with first “Close” operation of the movable mirror, the image preprocessing unit 112 reads the first still image from the CCD 101 and image processings are started in the image preprocessing unit 112. However, live view display is stopped since the pixel signal from the CCD 101 is continuously output in this period. Namely, the image preprocessing unit 112 is used for the processings of the still image for storage.
The image preprocessing unit 112 reads the image for live view from the CCD 102 and executes image processings from the time when reading process and image processings of the first still image in the image preprocessing unit 112 are completed. Then, the YUV data for display 132 which is stored in the main memory 120 by the image preprocessing unit 112 is read by the display control unit 114 and live view is started to be displayed.
Subsequently, when second “Open” operation of the movable mirror is started, live view display is stopped because the light from the subject is not incident on the CCD 102. In imaging of the second still image, live view display is stopped while the image preprocessing unit 112 reads the still image from the CCD 101 and executes image processings as in imaging of the first still image.
Thus, in the conventional single-lens reflex digital camera 100, live view display is stopped while the still image is continuously read since the image preprocessing unit 112 which operates as a sensor interface and an image processing unit switches to read images from two image sensors. During continuous shooting, therefore, a period of displaying live view is very short, and there has been a demand to improve operability during continuous shooting.
An invention disclosed in Japanese Patent Publication Laid Open Gazette No. 2007-243561 relates to a digital camera including the imaging element for the image for storage and the imaging element for the image for live view. This digital camera is designed to switch signals output from the two imaging elements by a selector and input the selected signal to control means for executing image processings. Therefore, live view cannot be displayed while image processings are being executed on a still image.
In some single-lens reflex digital cameras, imaging of the image for storage and imaging of the image for live view are realized using single imaging element. However, when the image for storage is started to be imaged, live view display is completely stopped until the transfer of the image data from the imaging element is completed. This leads to the fact that it takes long time to restore live view display after the imaging operation is executed.